Wednesday, 23 March 2016

Last week Dr.
Carys Bennett and TW:eed Team colleagues published their first paper from the
project in the journal Sedimentology on deposits containing tetrapods from
Scotland. We asked the questions: Why do these particular successions preserve
such abundant fossil evidence of the early terrestrial ecosystems? And what
sedimentary processes were acting to concentrate and preserve tetrapod fossils?
The study describes a particular type of sedimentary rock, sandy siltstones, as
sites of tetrapod fossil preservation. Sandy siltstones are matrix-supported
siltstones with millimetre sized lithic and bioclasts. They host concentrated fossil
deposits of tetrapods, fishes, sharks, arthropods, bivalves and plants.

Photographs of sandy siltstones from
the main field site and the Norham borehole

Members of
the team involved in the paper alongside myself are Sarah Davies, Tim Kearsey,
David Millward, Jenny Clack, Tim Smithson and John Marshall. In addition many
University of Leicester undergraduate and graduate volunteers have helped
examine samples in the lab that contributed to this research, and the following
are especially thanked for their efforts: Catherine Caseman, Rachel Curtis, Levi Curry, Rowan
DeJardin, Daniel Downs, Hattie Dulson, Deborah Fish, Susan Hammond, Catherine
Langford, Graham Liddiard, Jessica Mason, James Mawson, Christopher Stocker, Kirsty
Summers and Thomas Worthington.
Volunteers helped me examine many hundreds of rock samples and have also worked
on the microfossil aspects, with investigations ongoing.

Reconstruction diagram of conditions
on the floodplain when sandy siltstones formed

The Sedimentology
investigates why these deposits are formed and how tetrapods are preserved. The
conditions of their formation can tell us a lot of interesting information
about the ancient climate and the environment. Most sandy siltstones were
deposited on top of ancient soils or sun-cracked ground surfaces, indicating
they were the result of flooding events. The high frequency of these types of rocks
throughout the successions we have studied tells us that the floods were
regular, perhaps caused by an ancient Monsoonal climate. Tetrapods and
arthropods on land were washed away by the floods and transported into
temporary pools and lakes on the floodplain which were inhabited by fishes,
molluscs and other animals.

This reconstruction diagram by Mark Witton
gives a reconstruction of life on the ancient floodplains

This study is
the first to recognise these types of sediments as being important sites of
vertebrate fossil preservation – importantly for tetrapods, it will give
scientists some clues as to where they can look next!